If you enable GZIP compression, and try to connect a Crowd Client to the Crowd Server, the responses are uncompressed, and the content-encoding is unset.

Content-Encoding: 
Vary: 

Also, by leaving it unset, there is a conflict with mod_deflate + Apache when using mod_proxy where it'll output its headers as "Content-Encoding: , gzip" where the comma confuses the client (although you shouldn't really need mod_deflate if you've enabled gzip in Crowd).

Some searching shows that the problem is in atlassian-gzip, and it also affected JIRA: JRA-15658.

I tested upgrading my atlassian-gzipfilter library to 1.9 and that appeared to fix the problem where the contents were actually compressed, and the headers were properly written.